Synthetically enlarged camera aperture

ABSTRACT

Methods for obtaining a shallow depth of field effect (DOF) and improved signal-to-noise (SNR) in an image through synthetically increase the camera aperture of a compact camera using at least one actuator included in such a camera for other known purposes, for example for providing optical image stabilization (OIS). The synthetically enlarged camera aperture enables to take a plurality of images at different aperture positions. The plurality of images is processed into an image with shallow DOF and improved SNR.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional patentapplication 62/567,287 filed Oct. 3, 2017, which is incorporated hereinby reference in its entirety.

FIELD

Embodiments disclosed herein relate in general to digital cameras, andin particular to miniature folded and non-folded digital cameras.

BACKGROUND

Compact cameras, such as those that are incorporated in smartphones,have typically small apertures with a size of a few millimeters (mm)(e.g. 1-5 mm). The relatively small aperture of the camera (comparedwith cameras with larger aperture) causes at least the followinghandicaps:

a) the amount of light that can be absorbed by the camera image sensorin a given period of time is limited. This results in poor signal tonoise ratio (SNR) ratio when capturing an image in low light situations;and

b) the small aperture, when coupled with a relatively short focal length(e.g. 3-15 mm) due to the physical dimensions of the camera, causes arelatively wide depth of field (DOF). This is contrary to the shallowDOF or “bokeh” effect that is a sought-after property in smartphonedevices. Note that “shallow DOF” and “bokeh” are used hereininterchangeably.

In known art, the bokeh effect is achieved with a dual-camera setup, bycalculating a depth map from two camera images obtained from twoseparate cameras and by digitally blurring the images according to thedepth map.

Compact cameras in smartphones and other hand-held personal electronicdevices have different types of actuators. In an example, they oftenhave an optical image stabilization (OIS) actuator that can move thelens barrel (or simply the “lens”) of the camera in a plane parallel tothe image sensor plane. In folded cameras, in which an optical path froman object to be photographed is folded toward the image sensor by anoptical path folding element (OPFE), for example a prism, OIS is knownto be achieved by shifting the lens barrel laterally, in parallel to thesensor plane, or by tilting the prism (see for example co-ownedpublished international patent application WO2016166730).

SUMMARY

In the contexts of the following disclosure, DOF is defined as thedistance (in meters, cm, etc.) around the plane of focus (POF) in whichobjects appear acceptably sharp in an image. A shallow DOF is such thatthe distance is small (e.g. less than 20% of the object distance fromthe camera) and a wide DOF is such that the distance is large (e.g. morethan 30% of the object distance from the camera).

In various exemplary embodiments, there are provided methods forsynthetically enlarging a camera aperture and for obtaining shallow DOFeffects in folded and non-folded (also referred to as “upright”,“straight”, standing” or “vertical”) compact cameras using dedicatedand/or existing actuators, and in particular OIS actuators included insuch cameras. The miniature cameras for example in camera incorporatedin smartphones, tablet computers, laptop computer, smart televisions,smart home assistant devices, drones, baby monitors, video conferencerooms, surveillance cameras, cars, robots and other personalizedelectronic devices. Known OIS actuators, for example similar to thosedisclosed in co-owned published international patent applicationWO2016166730 (folded case) and see for example co-owned internationalpatent application WO20160156996 (non-folded case), may be “modified” byincreasing the size and/or length of their magnets and/or coils and/orrails to enable longer movement range (e.g. up to about ±2 mm) ofelements in folded and non-folded compact cameras. Henceforth, such OISactuators will be referred to as “modified OIS actuators”.

The following description refers to relative movements of one cameraelement (for example the lens, prism, or both) vs. another cameraelement (for example the image sensor) in an exemplary orthogonal XYZcoordinate system. The exemplary coordinate system is for reference andfor understanding inventive features disclosed herein, and should not beconsidered limiting.

The new use of dedicated and/or existing camera actuators in general andOIS actuators (regular or modified) in particular, coupled with an imageacquisition system and a post-processing algorithm, can syntheticallyincrease the size of the aperture, providing better signal-to-noiseratio (SNR) and a shallower DOF. The term “synthetically increasing” or“synthetically enlarging” as applied herein to a camera aperture refersto the camera aperture size being effectively (but not physically)increased by capturing different (e.g. a plurality N of) images with theaperture in (N) different positions. The camera aperture is shiftedlaterally relative to the sensor by a significant amount (for example bya few mm) and several images are captured, each with the aperturelocated in a different position relative to the sensor. To clarify, thephysical aperture size remains constant. Then, by aligning all capturedimages with respect to a certain in-focus object at a certain distancefrom the camera and by averaging them, objects outside the plane offocus will blur due to the parallax effect, thereby providing a shallowDOF effect. In some embodiments, the modifications to the OIS actuatorsto obtain modified OIS actuators enable large enough movement of theaperture of the optical system relative to the original position, sothat the resulting parallax effect will be significant, i.e. shallowerDOF by 10%, 20% or even 50% from the DOF of a single frame.

In exemplary embodiments there is provided a method comprising providinga camera that includes a camera aperture, a lens having a lens opticalaxis, an image sensor and an actuator, and operating the at least oneactuator to synthetically enlarge the camera aperture to obtain ashallow DOF effect and improved SNR in an image formed from a pluralityof images obtained with the image sensor.

In some exemplary embodiments, the actuator is an OIS actuator.

In some exemplary embodiments, the actuator is a modified OIS actuatorwith an extended actuation range. The extended actuation range may be arange of up to ±2 mm, and more specifically between ±1-2 mm.

In an exemplary embodiment, the operating the actuator to syntheticallyenlarge the camera aperture includes operating the actuator to move thecamera aperture to a plurality of positions, wherein each of theplurality of images is obtained in a respective camera apertureposition.

In an exemplary embodiment, the operating the actuator to syntheticallyenlarge the camera aperture includes operating the actuator to move thelens relative to the image sensor in a first direction substantiallyperpendicular to the lens optical axis.

In an exemplary embodiment, the operating the actuator to syntheticallyenlarge the camera aperture includes operating the actuator to move thelens relative to the image sensor in a second direction substantiallyperpendicular to the lens optical axis, wherein the second direction isnot parallel to the first direction.

In some exemplary embodiments, the first and second directions areorthogonal to each other.

In some exemplary embodiments, the camera is a non-folded camera.

In some exemplary embodiments, the camera is a folded camera.

In an exemplary embodiment, the camera is a folded camera that furtherincludes an optical path folding element (OPFE) that folds light from afirst optical axis to the lens optical axis.

In an exemplary embodiment in which the camera is folded the operatingthe actuator to synthetically enlarge the camera aperture includesoperating the actuator to move the camera aperture to a plurality ofpositions, wherein each of the plurality of images is obtained in arespective camera aperture position.

In an exemplary embodiment in which the camera is folded, the operatingthe actuator to synthetically enlarge the camera aperture includesoperating the actuator to move the lens relative to the image sensor ina first direction substantially perpendicular to the lens optical axis.

In an exemplary embodiment in which the camera is folded, the operatingthe actuator to synthetically enlarge the camera aperture includesoperating the actuator to move the lens relative to the image sensor ina second direction substantially perpendicular to the lens optical axis,wherein the second direction is not parallel to the first direction.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects, embodiments and features disclosed herein will become apparentfrom the following detailed description when considered in conjunctionwith the accompanying drawings, in which:

FIG. 1A shows an aperture and lens barrel centered relative to an imagesensor in a non-folded camera in (a) top view and (b) side view;

FIG. 1B shows the aperture and lens barrel of FIG. 1A after a lateralshift in a first direction relative to the image sensor in (a) top viewand (b) side view;

FIG. 1C shows the aperture and lens barrel of FIG. 1A after a lateralshift in a second direction orthogonal to the first direction relativeto the image sensor in (a) top view and (b) side view;

FIG. 2A shows an exemplary embodiment of a folded camera disclosedherein in (a) top view and (b) side view;

FIG. 2B shows the aperture, prism and lens barrel of the camera of FIG.2A after a lateral shift of the lens in a first direction relative tothe image sensor in (a) top view and (b) side view;

FIG. 2C shows the aperture, prism and lens barrel of the camera of FIG.2A after a shift of the prism in a second direction orthogonal to thefirst direction relative to the image sensor in (a) top view and (b)side view;

FIG. 2D shows the aperture, prism and the lens barrel of the camera ofFIG. 2A after a shift of the lens in a second direction orthogonal tothe first direction relative to the image sensor in (a) top view and (b)side view;

FIG. 3A shows schematically an example of 5 possible positions of thecamera aperture relative to the image sensor, corresponding to 5different frames captured by camera of FIGS. 1 and/or 2

FIG. 3B shows schematically an example of nine possible positions of thecamera aperture relative to the image sensor, corresponding to ninedifferent frames captured by a camera of FIGS. 1 and/or 2;

FIG. 3C shows schematically an example of three possible positions ofthe camera aperture relative to the image sensor, corresponding to threedifferent frames captured by a camera of FIGS. 1 and/or 2;

FIG. 4 shows in a flow chart stages of an exemplary method that uses asynthetically increased camera aperture to obtain a shallow DOF andimproved SNR.

DETAILED DESCRIPTION

FIGS. 1A-C show an exemplary embodiment of a camera 100 exhibiting asynthetically enlarged camera aperture disclosed herein. Camera 100 canbe exemplary an upright camera. Camera 100 comprises a lens 104 and animage sensor 106. Camera 100 may further comprise other elements whichare not shown for simplicity and are known in the art, such as:protective shield, infra-red (IR) filter, focusing mechanism (e.g.actuator), electrical connectivity, etc. Lens 104 may be for example afixed-focal-length-lens, characterized by an effective-focal-length(EFL), and an aperture 102. Aperture 102 defines the aperture of camera100, and the two terms (camera aperture and lens aperture) are usedherein interchangeably. The ratio between the EFL and the lens aperturediameter is known as the camera or lens “f-number”. For example, the EFLof lens 104 may be in the range of 3-15 mm. For example, the diameter ofaperture 102 may be in the range of 1-6 mm. For example, the f-number oflens may be in the range of 1.2-3.2. However, all these exemplarynumbers (EFL, aperture diameter, f-numbers) are not limiting. Camera 100also comprises a first actuator, which is not shown in the figures. Thefirst actuator may move (shift, actuate) lens 104 and aperture 102 withrespect to image sensor 106 in the X-Y plane (parallel to the imagesensor plane). Camera 100 may also include a second actuator (not shown)which may move (shift, actuate) lens 104 in the Z direction with respectto image sensor 106 for focusing purposes. In an example embodiment, thefirst actuator used for moving the lens may shift the lens in the X-Yplane, with a moving range on the order of ±2 mm along each axis. Thefirst and/or second actuators may be similar in structure to actuatorsused in a non-folded compact camera for OIS but with a significantlyincreased range, from (typically) a few hundreds of microns to an orderof +/−2 mm along each axis. In some embodiments, the first and/or secondactuator may be not similar to an OIS actuator. The followingnon-limiting description gives an example with the use of modified OISactuators, with the underling understanding that other methods ofactuations may be used. The significantly increased movement range maybe achieved by using current and known OIS technology (for exampleball-bearing voice coil motor (VCM) technology), with larger magnets andcoils and with longer rails, which allows a larger range of movement(e.g. in a range ±1-2 mm range of movement). Other actuation methods mayalso be applied, providing the lens can be shifted with the specifiedrange with respect to the sensor (e.g. stepper motors, piezoelectricmotors, shape memory alloy (SMA) actuators, etc.).

Returning now to FIGS. 1A-C, each figure shows the lens and lensaperture position vs. the image sensor from, respectively, a top view(a) and a schematic side view or 3D rendering (b). FIG. 1A shows uprightcamera 100 with aperture 102 and lens 104 centered vs. image sensor 106in an “original position”. FIGS. 1B and 1C show camera 100 with aperture102 and lens 104 shifted respectively in (a) in a first direction (+X)and in (b) in a second direction (−Y) relative to image sensor 106 (i.e.shifted in two orthogonal directions vs. an optical axis 110 parallel tothe Z direction, along which light enters the lens toward image sensor106). The shift of the lens from its original position in FIGS. 1B and1C can be in the range of a few mm, for example 2 mm. The two positionsin FIGS. 1B and 1C are only an example, and other shift directions andpositions are also possible in the X-Y plane, for example −X shift, +Yshift and a shift in a combined X and Y directions. In particular, notethat while shift directions described herein are orthogonal to eachother, in some embodiments shifts may occur in directions that are notorthogonal to other shift directions.

FIGS. 2A-D show an exemplary embodiment of a folded camera 200exhibiting a synthetically enlarged camera aperture disclosed herein.Each figure shows the aperture and lens position vs. the image sensorfrom, respectively, a top view (a) and a schematic side view or 3Drendering (b). Camera 200 includes a camera aperture 202, a lens 204, animage sensor 206 and an OPFE (for example a prism) 208. Like camera 100,camera 200 may include other elements not shown, for simplicity, and areknown in the art. FIG. 2A shows the “original position” of cameraaperture 202, centered on a first optical axis 210. In the foldedcamera, light entering the lens along first optical axis 210 is foldedto continue along a second optical axis 212 toward image sensor 206.FIG. 2B shows lens 204 shifted relative to image sensor 206 in a first(e.g. +Y) direction. FIG. 2C shows camera aperture 202 and prism 208shifted relative to lens 204 in a second direction (e.g. −X) which isorthogonal to the first direction. FIG. 2D shows lens 204 shiftedrelative to image sensor 206 in a third direction (e.g. +Z). The motiondirection shown in FIG. 2B-2D are only an example, and other shiftdirection may exist, in particular any linear combination of the shiftdirections shown.

In FIG. 2B, the lens is moved in a direction similar to that in FIG. 1B.In FIG. 2C, the lens is stationary, but the prism moves to create thesame optical affect as in FIG. 1C. In FIG. 2D, the lens moves in a thirddirection, resulting in an optical effect similar to that in FIG. 2C.

An actuator (not shown) as disclosed in co-owned published internationalpatent applications WO2016166730 (folded) and WO20160156996(non-folded), may be modified to increase the movement (range) of thelens barrel from a few hundreds of microns to a movement on the order of±2 mm, to enable shifting the aperture and/or lens along a firstdirection. The prism may be moved in a second direction, to bring itcloser or further away from the edge of the lens, thus also shifting thecamera aperture. In other words, in the exemplary coordinate systemsshown in FIGS. 1 and 2, a “longer range” modified OIS actuator can shiftthe lens and camera aperture by up to about ±2 mm in the X-Y directionsin a non-folded camera, and by up to about ±2 mm in the X-Y directionsor in Y-Z directions in a folded camera. The prism can be moved forexample using the same technology that is used to move the lens, but ina range that positions the prism closer/farther from the edge of thelens.

An exemplary method that uses a synthetically increased camera apertureto obtain a shallow DOF and improved SNR is provided with reference toFIG. 4. The exemplary method can be performed, for example, with acamera similar to camera 100 or camera 200:

Acquisition stage (FIG. 4, step 402): a plurality N of images of thesame scene is acquired in rapid succession (for example in 10-50 ms perimage, to prevent a significant object movement during the acquisitionprocess) when moving the position of the aperture between images, sothat each image is captured when the aperture is at a differentposition. In an example of an exposure rate of 10-60 ms, N wouldtypically be in the range of 3-9 frames. In an example of highillumination conditions, a high frame rate may be obtained such that Nmay be on the order of a few tens or even a few hundreds of frames.

FIG. 3A shows schematically an example of N=5 possible positions 302-310of the aperture relative to image sensor 106, corresponding to N=5different frames captured by the camera (e.g. camera 100 or 200). Inother examples, N may differ from 5. FIG. 3B shows schematically anexample of N=9 possible positions 312-328 of the aperture relative toimage sensor 106, corresponding to N=9 different frames captured by thecamera (e.g. camera 100 or 200). FIG. 3C shows schematically an exampleof N=3 possible positions 330-334 of the aperture relative to imagesensor 106, corresponding to N=3 different frames captured by the (e.g.camera 100 or 200).

In an embodiment, the first or second actuator may be a closed loopactuator, such that a position indication and a settling (i.e. arrivalof the actuator to the target position) indication may be provided tothe camera. In an embodiment, the exposure of the camera maybesynchronized with the motion of the actuator, such that the sequence ofN frames acquisition may be constructed from a repetitive stage of (1)frame exposure, (2) actuator motion to a new position, (3) actuatorsettling. Actuator settling may be such that the actuator does not shiftthe lens during exposure by more than 1 pixel, 2 pixels or 5 pixels.

Processing Stage: This Stage Includes Three Steps:

a) Frame stack alignment (FIG. 4, step 404): continuing the example instep 402, the N (e.g. 5) frames are aligned according to a certainregion of interest (ROI). Alignment may be performed using severalmethods. According to one example, a known frame alignment proceduresuch as image registration can be used. According to a second example,frames may be aligned by calculating the expected image shift resultedfrom known lens or prism shift. According to a third example, data froman inertial measurement system (e.g. a gyroscope accelerometer) may beused to calculate image shift caused by camera handshakes. Lastly, acombination of some or all the alignments above may be used. The ROI maybe the same ROI that was used to determine the focus of the camera, maybe an ROI indicated by a user via a user-interface, or may be chosenautomatically, by detecting the position of an object of interest (forexample, a face, detected by known face-detection methods) in the imageand by choosing the ROI to include that object of interest. Thealignment may compensate for image shifts. The alignment may alsoinclude distortion correction that can be introduced by the shifting ofthe aperture. The alignment may include shifting the images, or mayinclude cropping the images around some point, which may not be thecenter point of the image. After the alignment, all objects positionedin the same focus plane that corresponds to the object in the chosen ROIare aligned between the frames. Objects at distances outside that planeare misaligned.b) Frame averaging—(FIG. 4, step 406) the frames are averaged together,using for example a known procedure. In this averaging process, pixelsthat belong to aligned objects will not suffer any blur in the averaging(i.e. the resulting object in the output image will look the same as inany of the captured images, only with better SNR (approximatelyincreased by a factor √N, where N is the number of averaged images),while pixels that belong to misaligned objects will be averaged withmisaligned pixels and will therefore suffer blurring and will appearblurred in the output image. The blurring of object outside the focusplane will result in a shallower DOF, resulting DOF may be shallower by10%, 20% or 50% than the original DOF (of a single frame). The sameeffect occurs optically when the lens has a much larger aperture—theobject that is in the focus plane (i.e. in the depth position where thelens is focused at) is sharp, and objects in out-of-focus planes (i.e.outside the depth position where the lens is focused at) are blurry.Therefore, the proposed system synthetically enlarges the aperture.According to some example the system may discard some of the N frames,such that discarded frames are not included in the averaging. Discardingframes can be done for example due to blurry images, mis-focus of ROI,etc.c) Post processing (FIG. 4, step 408): extra stages of processing suchas refinement of the blur, adding additional blur, sharpening, etc., maybe applied on the synthetically-increased-camera-aperture output image,using for example a known procedure. The output of the camera mayinclude one or all of the original N frames in addition to thesynthetically-increased-camera-aperture output image.

Processing steps 404-408 may be performed immediately after frameacquisition step 402, or at later time. Processing steps 404-408 may bedone in the host device (e.g. in the host CPU, GPU etc.), or outside thehost device (e.g. by cloud computing).

The added blur for objects outside the chosen plane of focus (defined bythe object in the chosen ROI) will result in a shallow DOF effect in theoutput image, compared with any of the images in the stack (the inputimage to the algorithm). On the focused objects, the averaging of frameswill result in better signal to noise ratio compared with any of theimages in the stack.

While this disclosure describes a limited number of embodiments, it willbe appreciated that many variations, modifications and otherapplications of such embodiments may be made. In general, the disclosureis to be understood as not limited by the specific embodiments describedherein, but only by the scope of the appended claims.

All references mentioned in this specification are herein incorporatedin their entirety by reference into the specification, to the sameextent as if each individual reference was specifically and individuallyindicated to be incorporated herein by reference. In addition, citationor identification of any reference in this application shall not beconstrued as an admission that such reference is available as prior artto the present application.

What is claimed is:
 1. A method, comprising: a) providing a camera thatincludes a camera aperture, a lens having a lens optical axis, an imagesensor, and an actuator; and b) operating the actuator to syntheticallyenlarge the camera aperture to obtain a shallow depth of focus effect inan image formed from a plurality of images obtained with the imagesensor.
 2. The method of claim 1, wherein the actuator is an opticalimage stabilization actuator.
 3. The method of claim 1, wherein theoperating the actuator to synthetically enlarge the camera apertureincludes operating the actuator to move the camera aperture to aplurality of positions, wherein each of the plurality of images isobtained in a respective camera aperture position.
 4. The method ofclaim 1, wherein the operating the actuator to synthetically enlarge thecamera aperture includes operating the actuator to move the lensrelative to the image sensor in a first direction substantiallyperpendicular to the lens optical axis.
 5. The method of claim 4,wherein the operating the actuator to synthetically enlarge the cameraaperture includes operating the actuator to move the lens relative tothe image sensor in a second direction substantially perpendicular tothe lens optical axis and wherein the second direction is not parallelto the first direction.
 6. The method of claim 5, wherein the first andsecond directions are orthogonal to each other.
 7. The method of claim1, wherein the camera is a non-folded camera.
 8. The method of claim 7,wherein the actuator includes a modified optical image stabilization(OIS) actuator with extended actuation range.
 9. The method of claim 8,wherein the extended actuation range includes a range of up to ±2 mm.10. The method of claim 9, wherein the extended actuation range isbetween ±1-2 mm.
 11. The method of claim 3, wherein the camera is afolded camera that further includes an optical path folding element(OPFE) that folds light from a first optical axis to the lens opticalaxis.
 12. The method of claim 11, wherein the operating the actuator tosynthetically enlarge the camera aperture includes operating theactuator to move the lens relative to the image sensor in a firstdirection substantially perpendicular to the lens optical axis.
 13. Themethod of claim 12, wherein the operating the actuator to syntheticallyenlarge the camera aperture includes operating the actuator to move theOPFE relative to the image sensor in a second direction substantiallyparallel to the lens optical axis.
 14. The method of claim 12, whereinthe operating the actuator to synthetically enlarge the camera apertureincludes operating the actuator to move the lens relative to the imagesensor in a second direction substantially perpendicular to the lensoptical axis.
 15. The method of claim 11, wherein the actuator includesa modified OIS actuator with extended actuation range.
 16. The method ofclaim 15, wherein the extended actuation range includes a range of up to±2 mm.
 17. The method of claim 16, wherein the extended actuation rangeis between ±1-2 mm.
 18. A camera, comprising: a) a camera aperture; b) alens having a lens optical axis; c) an image sensor; and d) an actuatoroperative to synthetically enlarge the camera aperture to obtain ashallow depth of focus effect in an image formed from a plurality ofimages obtained with the image sensor.
 19. The camera of claim 18,wherein the actuator is an optical image stabilization (OIS) actuator.20. The camera of claim 18, wherein the actuator is operative tosynthetically enlarge the camera aperture by moving the lens to aplurality of positions, wherein each of the plurality of images isobtained in a respective camera aperture position.
 21. The camera ofclaim 18, wherein the actuator is operative to synthetically enlarge thecamera aperture by moving the lens relative to the image sensor in afirst direction substantially perpendicular to the lens optical axis.22. The camera of claim 21, wherein the OIS actuator is operative tosynthetically enlarge the camera aperture by moving the lens relative tothe image sensor in a second direction substantially perpendicular tothe lens optical axis and wherein the second direction is not parallelto the first direction
 23. The camera of claim 22, wherein the first andsecond directions are orthogonal to each other.
 24. The camera of claim18, wherein the camera is a non-folded camera.
 25. The camera of claim18, wherein the actuator includes a modified OIS actuator with anextended actuation range.
 26. The camera of claim 25, wherein theextended actuation range includes a range of up to ±2 mm.
 27. The cameraof claim 25, wherein the extended actuation range is between ±1-2 mm.